US 20050243855 A1
At a base station receiver in a CDMA wireless communications system, in order to reduce reliance on the parameter values transmitted on a packet data control channel (PDCCH) to properly detect the high speed packet data transmitted on a packet data channel (PDCH) with which the PDCCH is code-division-multiplexed, data detection is performed using different possible values for at least one of the parameters and determining if a data packet derived from the PDCH detected under the different values produces a detected data packet that passes a CRC check. If a data packet derived from the received PDCH using a possible parameter value passes the CRC check, then the data packet is delivered to the output and an ACK is transmitted back to the transmitting mobile terminal.
1. A method comprising the steps of:
detecting received data in accordance with the value of at least one parameter that is associated with the data, the at least one parameter having a plurality of possible discrete values;
characterized in that the method further comprises:
detecting the received data in accordance with different assumed possible parameter values;
determining for each different assumed parameter value if the data detected in accordance with that assumed parameter value passes a CRC check; and
if the data detected in accordance with an assumed parameter value passes the CRC check, delivering that detected data to an output.
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10. A receiver comprising:
detecting means for detecting received data in accordance with the value of at least one parameter that is associated with the data, the at least one parameter having a plurality of possible discrete values, the detecting means detecting the received data in accordance with different assumed possible parameter values; and
means for determining for each different assumed parameter value if the data detected in accordance with that assumed parameter value passes a CRC check, and if the data detected in accordance with an assumed parameter value passes the CRC check, delivering that detected data to an output.
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This invention relates to wireless communications, and more particularly, to detecting at a base station the high-speed Packet Data Channel that is transmitted on the reverse link by a mobile terminal.
Mobile terminals that are in accord with the latest 3GPP2 CDMA2000-1x EVDV standards (RevD) support high-speed uplink data transmission that allow partial retransmission of a transmitted data packet at the physical layer unlike previous releases which performed retransmission decisions at higher layers that incurred a greater latency. In accordance with these latest standards, high speed data transmission from the mobile terminal takes place over a Packet Data Channel (PDCH), which is code division multiplexed with a Packet Data Control Channel (PDCCH) and a Pilot Channel (PICH) for uplink transmission to the base station. At the mobile terminal, Cyclic Redundancy Check (CRC) bits are attached to a data packet that is to be transmitted. For example, a 16-bit CRC is appended to each data packet. The resultant combined data and CRC bits are turbo encoded and then interleaved, the latter to combat a correlated fading channel. The interleaved bits are then reorganized into N subpackets, where N is the total number of transmissions allowed for one data packet, which is three in accordance with the afore-noted standards. Each subpacket takes part or the entire data from the output of the interleaver. The rules for forming the subpackets for each data packet are known to the mobile terminal and to the base station if the data packet size is known. All subpackets associated with one data packet have the same size and can be overlapped. For one data packet, each transmission to the base station consists of one of the subpackets, which are consecutively numbered with a subpacket ID number (SPID) from 0 to N-1. If the mobile terminal does not receive an acknowledge message (ACK) from the base station, transmission by the mobile terminal continues one subpacket at a time until an ACK is received in response to a transmitted subpacket, or all N subpackets have been transmitted, whichever occurs first. If an ACK is not received after all N subpackets have been transmitted, the mobile terminal's higher layer then decides whether to resend the packet in smaller size packets or a same size packet again, subpacket-by-subpacket as was just done, or to just drop its attempt to transmit the packet.
In transmitting a packet to the base station, the mobile terminal first transmits subpacket number 0, which is modulated and code-division-multiplexed (CDM-ed) with the PICH and the PDCCH, with proper levels relative to the PICH. As will be discussed, the PDCCH transmitted with the PDCH includes information needed by the base station receiver to properly decode the subpacket. This information includes the SPID, the size of the input data packet, and an indication of a PDCH-to-PICH power ratio. At the base station, the received code-division-multiplexed signal is despread and demodulated to generate soft symbol metrics for the PDCH. If SPID=0, then the generated soft symbol metrics are passed through a deinterleaver and a turbo decoder to reform the bits within the transmitted data packet and its associated attached CRC bits. A CRC check is then performed on the decoded data bits to determine whether there is a match between the CRC calculated from those decoded data bits and the attached decoded CRC bits. If the CRC calculated from the received decoded data bits matches the decoded CRC (a CRC pass), it is assumed with high probability that the data bits have been received and decoded accurately. If there is not a match (a CRC fail), then it is assumed that the received data bits are not the same as the transmitted bits in the input data packet. The pass or fail result of the CRC is passed to the downlink ACK channel processing. If the CRC is a pass, then an ACK is sent to the mobile station; otherwise no ACK is sent to the mobile terminal.
If the mobile terminal detects an ACK from the base station over the downlink ACK channel, it considers the transmission to have been successful and processes the next data packet to be transmitted from the higher layer. If the mobile terminal does not receive an ACK, then it does not receive a new data packet from the higher layer and transmits the next subpacket, which has SPID=1, from the original transmitted data packet. At the base station this next received subpacket is despread and demodulated to generate soft symbol metrics. The soft symbol metrics are then subpacket-combined with the soft symbol metrics previously received for the subpacket having SPID=0. If subpacket SPID=0 and subpacket SPID=1 have overlapping data bits, accumulation of the soft symbol metrics is performed on the soft symbols corresponding to the overlapped bits. After combination, the resultant metrics are then deinterleaved and turbo-decoded. As before, a CRC check is performed on the resultant decoded bits. If the CRC results in a pass, the base station sends an ACK to the mobile terminal; otherwise the base station is silent. If a CRC fail results again, the mobile terminal transmits its last remaining subpacket, which has SPID=2, to the base station and the process is repeated again. This time the subpacket combining at the base station undoes the packet formation at the mobile station plus the combining, if necessary, over subpackets SPID=0, 1 and 2.
As afore-noted, in accordance with 3GPP2 standards, the maximum number, N, of subpacket transmissions for one data packet is three. Thus, if a CRC fail still results after the third subpacket transmission, the higher layer will decide whether to abandon transmission of this data packet or to transmit it again. In either case, the next data packet received from the higher layer, be it this same data packet being provided for retransmission the same data in smaller size packets or a totally different and new packet, is treated as a new packet at the physical layer.
As previously noted, the PDCCH carries information needed by the base station to properly recover the transmitted subpacket on the PDCH and from that or multiple subpackets, the transmitted data packet. In the 3GPP2 system, subpacket formation is dependent on the input data packet size. In addition, the maximum number of transmissions of subpackets per data packet is a fixed parameter in the 3GPP2 standards. As noted above, that number is three. In addition an indication of the PDCH-to-PICH power ratio is required for turbo decoding. In 3GPP2 standards, there are only two possible PDCH-to-PICH power ratios for one data packet size. Further, in order to properly decode a subpacket, its SPID needs to be known to enable the receiver to properly combine a de-segmented packet with the one or two previously received subpackets if its SPID is 1 or 2, respectively. Thus, in order to properly detect the PDCH and recover the transmitted data packet, the following information needs to be associated with each received PDCH: the data packet size; the subpacket SPID; and the PDCH-to-PICH power ratio. As is specified in the standards, this information is carried by the PDCCH in order to assist PDCH processing and is transmitted simultaneously with the PDCH subpacket whose information it is carrying and with which it is code-division-multiplexed.
At the base station receiver, the PDCCH carrying this needed information is demodulated and decoded prior to processing of the PDCH to enable the receiver to properly detect the PDCH and recover the transmitted data packet. Using the PDCCH to provide these parameters, however, has several disadvantages. Firstly, using the PDCCH contributes to the total interference level within a cell and therefore reduces the uplink capacity. Secondly, in order to achieve a certain frame error rate (e.g., an order of magnitude smaller than a PDCH target frame error rate), the PDCCH needs to be transmitted at a sufficiently high power level, which further degrades uplink capacity. If the PDCCH is not transmitted at a high enough power level, then an error in detecting the transmitted SPID, for example, can have a deleterious effect on the latency in recovering the PDCH. For example, if the base station detects the PDCCH and it indicates an SPID of 0 and a CRC fail results in decoding the PDCH, the base station will not send an ACK and will wait to receive the next subpacket from the mobile terminal. If the PDCCH associated with that next received subpacket indicates an SPID of 2, an error has occurred somewhere because the next subpacket should have an SPID of 1. In fact, the only way that the PDCCH for the next received subpacket could properly indicate an SPID of 0 would be if the mobile terminal had erroneously detected an ACK when base station had in fact sent nothing, and the mobile terminal in response to that detected ACK had transmitted the first subpacket of the next data packet. The probability, however, of detecting an ACK when the base station had in fact sent nothing is low if the downlink ACK channel is reliable. Thus, when an SPID is received in error, the transmitted information on the PDCCH has likely been corrupted. The base station in detecting the received PDCCH, however, only looks at the information contained in the currently received PDCCH and not simultaneously at previous ones and thus is unable to detect that something is in error. Thus, when it receives a PDCCH with an SPID of 2, it will incorrectly combine the soft metrics in the currently received subpacket with the soft metrics in the two previously received subpackets, resulting in a CRC fail on the reconstructed data packet. As a result, extra latency is added to the recovery of the PDCH since the data packet will likely have to be retransmitted in its entirety again. In order to have a negligible impact on system throughput, the probability of incorrectly receiving critical information in the PDCCH should be an order of magnitude smaller than the PDCH target error rate. To achieve this, the PDCCH power needs to be at a sufficiently high level, which as aforenoted, results in a degradation in uplink capacity.
A methodology of detecting the uplink packet data channel that is less reliant on receiving a high-powered supplemental packet data control channel is thus desirable.
In accordance with an embodiment of the present invention, reliance on the parameter values transmitted on the PDCCH to properly detect the PDCH at the base station receiver is reduced by using different possible discrete values for at least one of the parameters and determining if a data packet derived from the PDCH detected under one of the possible values of the at least one parameter produces a detected data packet that passes the CRC check. If a data packet derived from the received PDCH using a possible parameter value passes the CRC check, then the data packet is delivered to the output and an ACK is transmitted back to the mobile terminal.
In a first embodiment, reliance on the PDCCH is eliminated by detecting the PDCH based on all possible combinations of PDCCH parameter values that are supported by the base station. As aforenoted, these parameters include the SPID, the size of the input data packet, and an indication of PDCH-to-PICH power ratio. Only specific discrete values of these parameters are supported. Further, only a subset of all combinations of these discrete values may be supported by the base station and mobile terminal. By assuming each of the allowed and supported combinations of these values, and decoding the received PDCH input in accordance with each of these combinations, a determination is made if any such combination of these parameters yields a detected data packet that results in a CRC pass. If a resultant data packet can be unambiguously attributed to one combination of parameters or more than one combination that have the same packet length and SPID number, then that data packet is delivered to the output and an ACK is sent to the mobile terminal. In this embodiment, since the PDCCH is not relied on at all for PDCH processing at the mobile terminal, the base station can instruct the mobile terminal to set its PDCCH to PICH power ratio to zero, thereby totally precluding any deleterious effect on uplink capacity by the PCDDH.
In a second embodiment, the PDCCH is used and detected and at least one of the transmitted parameters contained within the PDCCH about the PDCH are used to detect the PDCH data while at least one other parameter is allowed to assume each of its possible discrete values. A data packet is then separately detected using the PDCCH-detected parameter value or values and each discrete value or combination of values of the other parameter or parameters. A CRC check is then performed on the resultant detected data packet under each discrete value or combination of values of that parameter or parameters in order to determine if using such parameter value or values in combination with the other parameter value or values detected from the PDCCH produces an output data packet that yields a CRC pass. Specifically, the information in the received PDCCH relating to the parameters of packet length and PDCH-to-PICH power ratio are used to detect the PDCH together with each possible discrete SPID. Since, as aforenoted, in 3GPP2, SPID has three possible values, the PDCH is detected separately for each of the three SPID values and a determination is made whether the resultant detected data packet passes the CRC check. If it does, the detected data packet is delivered to the output.
With reference to the block diagram in
As previously noted, in the 3GPP2 system subpacket formation is dependent on data packet size. Once the data packet size is specified, subpacket formation is known. The maximum number of transmissions for a data packet, three, is also a fixed parameter. In order to detect the PDCH at the base station receiver the data packet size, the subpacket number, SPID, being transmitted and the PDCH-to-PICH power ratio are transmitted by the PDCCH at the same time and code-division-multiplexed with the PDCH subpacket show information it is carrying.
At base station receiver 103, despreader 112 demultiplexes the received CDM-ed signal generating the modulated PDCH, the PDCCH and the PICH. Demodulator 113, using the packet size information in the PDCCH demodulates the PDCH to generate soft symbol metrics for the PDCH. Subpacket combiner 114, using the packet size and the SPID from the PDCCH, then performs the reverse function of subpacket former 107 on these soft symbol metrics. Combiner 114 places each symbol at a bit position corresponding to the output of the interleaver 106 in mobile terminal transmitter 101. If overlapped data has been transmitted, combining is also performed by combiner 114 on soft symbols corresponding to the overlapped bits. The resultant metrics are then passed through deinterleaver 115, which also uses the packet size in the PDDCH as an input. Turbo decoder 116, using the packet size and the PDCH-to-PICH power ratio provided via the PDCCH, outputs a decoded block of bits comprising a data part and a CRC part. A CRC check 117 then checks to see whether the CRC calculated on the data part of the decoded data block at the output of turbo decoder 116 matches the CRC part. If it does, the data part is outputted as the recovered packet data on output 118 and a CRC pass is outputted on output 119. That CRC pass is transmitted as an ACK signal on downlink ACK channel 120 to mobile terminal transmitter 101. If a CRC fail is generated by the CRC checker 117, then nothing is transmitted back to the mobile terminal transmitter 101.
At mobile terminal transmitter 101, when an ACK is detected, the transmission is considered successful and a next packet to transmit is received from the higher layer on input 102. If no ACK is received by mobile terminal transmitter 101 over downlink ACK channel 120, then the mobile terminal does not receive any new data packet from the higher layer and now transmits subpacket 1 from the same original data packet. When subpacket 1 is received by base station receiver 103, it is despread and demodulated to generate soft symbol metrics. Subpacket comber 114 performs the reverse function of subpacket former 107, but combines the received soft symbol metric now received for subpacket 1 with the previously received soft symbol metrics for subpacket 0, where each symbol from subpackets 0 and 1 is placed at the corresponding bit positions corresponding to the output of interleaver 106 at the mobile terminal transmitter 101. If overlapped data is transmitted, combining is also performed on soft symbols corresponding to overlapped bits. As with subpacket 0, the resultant metrics are deinterleaved, turbo decoded, and CRC checked. If the CRC check results in a pass, then an ACK is sent downlink to the mobile terminal transmitter 101 and a new packet is inputted from the higher layer. If a CRC fail results again, then the base station receiver 103 sends nothing and a last attempt to transmit the current packet via transmission of subpacket 2 is made by the mobile terminal transmitter. Subpacket combining by combiner 114 is now performed over both of the previously received subpackets 0 and 1 with the now received subpacket 2.
With reference again to
In the first embodiment of the present invention, receipt of the information in the PDCCH is not relied on at all. In fact the PDCCH-to-PICH power ratio is a programmable parameter that is specified by the base station and can be set to zero so that it is not transmitted by the mobile terminal thereby precluding any deleterious effect on the uplink capacity.
In the first embodiment each of the possible 60 modes are “tested” against the received PDCH to determine if using the parameter values associated with a particular index produces an output data packet that passes a CRC check. Since all PDCH encoder packets are protected by a 16-bit CRC, perfect error detection can be assumed as compared with a target PDCH frame error rate. In this embodiment, functionally illustrated in
The flowchart in
The above-described embodiment would be most useful when only a subset of the active modes are supported in a system, as for example, 10 modes of the 60 possible modes indicated in the table of
If power is available for the transmission of the PDCCH, but not at a sufficiently high level to guarantee an error performance that is an order of magnitude better than the desired PDCH error performance, then the above-described embodiment can be simplified so as to use some of the parameter values in the received and detected PDCCH while at least one of the other parameters is cycled through each of its possible values and a CRC check is performed on the detected PDCH packet for each such parameter value.
With reference to
With reference again to
From the despread PDCH subpacket data on input 605, the PDCH data is detected for an assumed SPID of 0, 1 and 2, using the corresponding PDCH information derived from the PDCCH soft symbol metrics for each SPID. Since the PDCH data from the currently received PDCH may need to be combined with previously received PDCH data depending on the assumed SPID, the current PDCH data is stored in subpacket buffer 605 while the previous PDCH data and previous previous PDCH data are stored in subpacket buffers 607 and 608, respectively.
In testing the received PDCH on the assumption that its SPID=0, PDCCH detector 609 detects the PDCCH soft symbol metrics associated with the current subpacket that are stored in a subpacket buffer 602. Detector 609, assuming the current PDCH to have an SPID of 0, performs a 64-FHT followed by a search for the maximum metric over only the 20 PDCCH indexes in the table in
In testing the received PDCH on the assumption that its SPID=1, the current received PDCH and associated PDCCH and the previous received PDCH and associated PDCCH are used in decoding both the PDCH and PDCCH. In decoding the PDCCH, PDCCH detector 615 separately performs a 64-FHT on the previous PDCCH soft symbols stored in buffer 603 and the current PDCCH soft symbols stored in buffer 602. The 20 PDCCH output metrics associated with the previous PDCH having indexes associated with SPID=0 (indices 0-10 and 33-41 from the table in
In testing the received PDCH on the assumption that its SPID=2, the current received PDCH and associated PDCCH and the two previously received PDCHs and associated PDCCHs are used in decoding both the current PDCH and PDCCH. In decoding the current PDCCH, PDCCH detector 620 separately performs a 64-FHT on the two previous PDCCH soft symbols stored in buffers 603 and 604 and the current PDCCH soft symbols stored in buffer 602. The two 20 PDCCH output metrics associated with the two previous PDCHs having indexes associated with SPID=1 (indices 11-21 and 42-50 from the table in
The detected PDCH data and associated CRC check derived under each of the three SPID parameter values are inputted to a PDCH data and CRC reporter 625, which decides from the three reported CRC checks whether or not to output one of the detected PDCH data and to send an ACK to the mobile terminal. A flowchart illustrating the functions of reporter 625 is shown in
While the particular invention has been described with reference to the illustrative embodiment, this description should not be construed in a limiting sense. It is understood that although the present invention has been described, various modifications of the illustrative embodiments, as well as additional embodiments of the invention, will be apparent to one of ordinary skill in the art upon reference to this description without departing from the spirit of the invention, as recited in the claims appended hereto. Although described in conjunction with 3GPP2 CDMA2000-1x EVDV/EVDO standards, the present invention could be implemented in any CDMA or non-CDMA type of wireless system, including, by way of example, UMTS and CDMA2000-1x EVDV. Further, the invention may be implemented in different locations, such as a base station (NodeB in UMTS terminology), a base station controller (a Radio Network Controller [RNC] in UMTS terminology) and/or a mobile switching center (a mobile service switching center [MSC] in UMTS terminology), a mobile terminal (UE in UMTS terminology), or elsewhere depending upon in what type of system the invention is employed. Furthermore, the invention can be implemented in any type of data communication system, wireless or hard-wired, including an optical communications system, in which detection of transmitted data is dependent on one or more parameter values that are associated with the transmitted data. Moreover, processing circuitry required to implement and use the described invention may be implemented in application specific integrated circuits, software-driven processing circuitry, firmware, programmable logic devices, hardware, discrete components or arrangements of the above components as would be understood by one of ordinary skill in the art with the benefit of this disclosure. Those skilled in the art will readily recognize that these and various other modifications, arrangements and methods can be made to the present invention without strictly following the exemplary applications illustrated and described herein and without departing from the spirit and scope of the present invention. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.